Upper course features

As the river moves through the upper course it cuts downwards. The gradient here is steep and the river channel is narrow. Vertical erosion in this highland part of the river helps to create steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.

As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip.

When a river runs over alternating layers of hard and soft rock, rapids andwaterfalls may form.

Middle course features

MeandersA meander on the River Cuckmere

In the middle course the river has more energy and a high volume of water. The gradient here is gentle and lateral (sideways) erosion has widened the river channel. The river channel has also deepened. A larger river channel means there is less friction, so the water flows faster:

As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders.

The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream.

The force of the water erodes and undercuts the river bank on the outsideof the bend where water flow has most energy due to decreased friction.

On the inside of the bend, where the river flow is slower, material isdeposited, as there is more friction.

Over time the horseshoe become tighter, until the ends become very close together. As the river breaks through, eg during a flood when the river has a higher discharge and more energy, and the ends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lake.

Oxbow lakeIn the animation above, upstream a large bend becomes a horseshoe and is eventually cut-off to become an oxbow lake. Downstream the river is eroding its outer bank and depositing on its inner bank to create a new meander.

Lower course features

In the lower course, the river has a high volume and a large discharge. The river channel is now deep and wide and the landscape around it is flat. However, as a river reaches the end of its journey, energy levels are low and depositiontakes place.FloodplainsThe river now has a wide floodplain. A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the richalluvium deposited by floodwaters. This makes floodplains a good place for agriculture. A build up of alluvium on the banks of a river can create levees, which raise the river bank.DeltasDeltas are found at the mouth of large rivers - for example, the Mississippi. A delta is formed when the river deposits its material faster than the sea can remove it. There are three main types of delta, named after the shape they create:Three main types of delta

Transportation

Erosional featuresInterlocking Spurs - As the river cuts its deep V-shaped valley in its upper course, it follows the path of the easies trock to erode. Thus it tends to wind its way along, leaving the more resistant areas of rock as interlocking spurs.Meanders - Meanders occur in the mid course and lower course of the river, where it is beginning to cut laterally as it gets closer to base level. Meanders are basically bends in the river, where the faster water on the outside of the bend has cut into the bank, eroding it and creating a river cliff. At the same time the slow moving water on the inside of the bend deposits its load, building up a shallow slip-off slope. Meanders migrate downstream as they cut through the valley sides.This creates a line of parallel cliffs along the sides of the valley.Ox-Bow Lakes - In the lower course of theriver meanders can become so pronounced that they can form ox-bow lakes. Inthe lower course the rapid lateral erosion cuts into the neck of the meander, narrowing it considerably. Eventually the force of the river breaks through the neck, and as this is the easiest way for the water to go, the old meanderis left without any significant amount of water flowing through it. Quickly the river deposits material along the side of its new course, which completely block off the old meander, creating an ox-bow lake.V-shaped valleys - In the upper course ofthe river, it cuts rapidly downwards, as the river puts almost all of its energy towards cutting down to base level. This causes the most distinctive river feature, the V-shaped valley. Rocks and other material are washed into the river from the steep valley sides during times of heavy rainfall, adding to the material being carried by the river.Waterfalls - Waterfalls are perhaps the most spectacular erosional feature of a river. They primarily occur in the upper course of the river. Often a waterfall will form where a band of harder rock lies over a softer one. As the river flows over the edge of the harder, more resistant rock, into its plunge pool, it erodes away the softer rock below, creating an overhang. Once the overhang is big enough the whole thing collapses due to gravity and its own weight. The whole process then occurs again. This means that over time waterfalls will move backwards up the valley, leaving a steep sided gorge in front of them.

Depositional featuresDeltas - Deltas occur where a river that carries a large amount of sediment meets a lake or the sea. This meeting causes the river to lose energy and drop the sediment it is carrying. Deltas form two types, called arcuate and birds foot. An arcuate delta is one, which builds out into the sea, extending the coast line, as the Nile Deltadoes in Egypt. A bird's foot delta is an extension of this as "fingers"of material form further off the edge of the delta. The delta of the Mississippi river shows these characteristics.Flood Plain - The Flood Plain is the area of alluvial deposits found beside the river in its lower course. As meanders move slowly down the course of the river they erode away the valley to create a wide valley floor, and they deposit layers of alluvial material on the slip off slopes. Over time this builds up into a large flood plain. A very good example is the Canterbury Plains in New Zealand, where many large rivers have contributed to a huge area of alluvial deposition that has become prime agricultural land.Levee's - Levees are naturally formed banks along the sides of a river channel in its lower course, as it flows through the flood plain. They are formed by the river depositing material when it floods. During a flood the river deposits its heaviest, coarsest material closest to its normal course. Over years this deposition has built up the natural embankments, built of coarse material. Beyond them the flood plain has been built up of the finer material that was deposited further away from the normal course of the river.Features overview

[/ulist]Upper CourseMid CourseLower CourseFeaturesInterlocking spurs, waterfalls, V-shaped valley, gorges.Meanders, Slip-off slopes, ox-bow lakes.Deltas, flood plains, levees, meanders, ox-bow lakes.VelocityRelatively slow moving. Despite areas of fast flowing water, the large amount of material on the river channel bed means that friction will slow the water down.The water has increased in speed as the channel widens and becomes smoother. Some boulders cause friction to slow it down a little.The fastest section of the river, as the channel is widest, with very smooth sides, and the greatest volume of water.

Deposition

Deposition is when the river loses energy, and it can't carry as much load. It drops its load (material it has been carrying), starting with the largest particles.

Load

The load is any material transported by the river, e.g. Sand, pebbles, rock particles.

Meander

A Meander is a winding curve in a river.

Weathering

Weathering is the wearing away of rocks. It can be weathering, biological or physical weathering.

Infiltration

Infiltration is the downward movement of water that seeps into the soil or permeable (also called porous) rock at ground level.

Permeable

Permeable materials are materials that water can pass through, e.g. limestone.